Production of pulp



Dec. 29, 1936. T. L. DUNBAR Re. 20,217

PRODUCTION OF PULP Original Filed April 16, 1932 ATTORN Y Reissued Dec.29, 1936 UNITED STATES PATENT OFFICE PRODUCTION OF PULP Thomas LeonidasDunbar, Watertown, N. Y assig-nor to Chemipulp Process, Incorporated,Water-town, N. Y., a corporation of New York 19 Claims.

This invention relates to the production of pulp, and in. particular tothe production of a super-quality sulphite pulp for use in themanufacture of paper.

- It is an object of my invention to provide a process capable ofproducing a sulphite pulp from which may be made sulphite paper ofunusually high strength. a

A further object is to provide a process for the production of ,sulphitepulp capable of giving a higher yield of pulp than is obtainable byprocesses now in use.

' Further, it is my object to produce a highcellulose pulp from whichmay be made a paper similar to kraft in strength, but more pliable thankrai't.

A further object is the provision of a flexible process capable ofvariation of producing pulp with varying characteristics as may be.desired.

A still further object is the provision of a sulphite process by the useof which a saving of acid is effected.

The higher strength of kraft pulp is due primarily to residual'ligninwhich is not removed by the kraft process. While my improved processremoves the greater part of this residual lignin and pentosans, in doingso it leaves a cellulose of unusually high strength, thereby impartinghighly desirable characteristics to the finished prod- Briefiy, in thepractice of my improved process the digester is first filled with rawmaterial and bisulphite liquor in accordance with the disclosure of myUnited States Patents Nos. 1,646,084 and 35 1,669,234 and Dunbar et a1.U. 8. Patent No. 1,699,056. A working pressure and temperaturesufllcient to release extractives from the raw .material is then builtup and the digester is closed in for a soaking period suitable to thewood con- 40 ditions as hereinafter pointed out. The-bisulphite liquoris then drained from the digester and may be conducted to the acidsettling tank or to other parts of the acid system where partiallyprepared liquor is contacted with liquors from the 45 digester. The rawmaterial is then subjected to a bisulphite cook in accordance withprinciples hereinafter set forth. At the termination of this cook, thematerial is subjected to a further treatment with precipitated alkalinewater.

5 The accompanying drawing is a diagrammatic view of apparatus-suitablefor the practice of my improved process.

In the drawing, I is a milk of lime acid tower. This is shown by way ofexample only, as the 5s applicability of my invention is not limited tothe milk of lime system, but is equally applicable to the limestonetower system. 2 is a line leading from the tower l to the settling tank3. From the settling tank, the line 4 leads to the pump 5, which forcesthe liquor into the acid storage 5 tank 1 through the line 6. The pump 0forces the liquor from the storage tank 1 through the line 9 to theeductor i0, where it is contacted with relief fluids from the digestersi5. Although four digesters are shown, any number may be used.

- The drop or condenser leg 'leads from the eductor I0 through theexchange heater 23 to the bottom of the accumulator l I. i2 is a pumpfor forcing the bisulphite liquor into any one of the digesters asrequired, by means of line Hand 15 the valved branch filling lines ll.2| is an exchange heater interposed in the line IS. a

I6 is a valved branch leading from the top of each digester for ventingrelief gases and fluids through the header IT to the eductor VI 0, while22 20 is a valved side relief branch for conducting liquors from thedigester to the header ii. The valved branch line 25 leads from the topof the digester to the header 21, which header discharges into the acidstorage tank I. 26 is a valved 25 branch of! from the line 25, ventingto the atmosphere. The operation of; these vent lines has been fullydescribed in my copending application Ser. No. 446,046, new Patent1,859,384 dated May 24, 1932.

Liquor may be drained from the digesters through the strainer l8, theline 20 having therein the valve i9, and the header 2| leading back tothe settling tank I.

In the practice of my improved process, I may proceed as follows: 1 l

The digester having been charged with chips,

the valve in the branch 28 is opened and the digester is filled with hotpreconditioned bisulphite liquor, heated to a temperature of 10 C. ormore, 40 from the accumulator II by means of the pump i2, line It andvalved branch I 4, in accordance with the disclosure of my copendingapplication, Ser. No. 446,046. when the digester has been filled, thevalve in the branch 261s closed and a pressure of approximately poundsis applied to the contents of the digester by running the pump l2 untilthis has been accomplished. The valve in the line II is thenclosed andthe pump l2 shut down, and the chips are subjected to a 50 soaking orpenetration period under pressure,

' with all the valves of the digester lines closed.

The duration of this soaking period, as well as v the temperature, willvary with the kind and quality of .the raw material. and with itsinitial moisture content, this soaking period being prefersbly continueduntil the extractives (by which I mean the so-called water-solubles")are reloasedfromthematerialandalltherawmaterial- I ispiacedinaconstantstate asregardsmoisture content. The bisulphitc liquorpenetrates the chills. to scene extimt, leaving a deposit of acid 10addition, this initial penetration may partiallythesucceedingstageoftheprocess.

At the termination of this w: a period, the

bisulphite liquor is drained out of the digester.

16 through 20 and is returnedinthebisulphitellquordrainedbacktothesettlirutsnkareneutralisedbyanexcessofalkalinebsseintherswliquon' After the soaking period has been completedandthellquorhasbeendrainedirom thedigester, the digesteris again filledwith hot bisulphite liquor, steam is admitted tothe digester,

through line (not shown) and the cooking 'is carriedon'intheusualmanneruntil alargepart ntent of the wood is removed. 'lh'isstage of my improved process diil'ers,however,fromtheacidcookaspracticedinthepresent single-stale process. Inthe single-stage procms, the extractives, resinous matter and lignln aresubstantially dissolved out by acid. This produces, particularly towardthe end of the cook, chemical which have aideteriorating elect onthefibres. Inmy improved processthe fonnationofthese compoundsistoalargeextent prevented.duetothefactthatupontheirappearanceinquantities whichwould injurethe cellulose,thecookisstopped,allorapartof thethematerialisthentreatedinathirdstagewith lime (or other suitablealkaline) water. The

. Ihavefoundthatitissometimesdesirable,in

ordertopmducespecialgradesofpulp,torepeatthecoohorsecondstageofmyprocess.In thhcssaapsrtonlyofthiscookisaccomplished with each separate charge ofbisulphite liquor 79 and consequently there is a progressive increase inthe maflmum temperature for each recooking. For example. I have foundthat in the production of a sulphlte pulp with the strengthcharacteristicsctahighgradekraftpulnthecook'"ihelfmaybecarriedominthreestageathe maximum temperature during thefirst being 110' 0., during the second approximately 120 C. and

during the third approximately 132 C.

After the completion of the cook, the valve I.

is again openedand all or part of the digester I liquor is drained backto the settling, tank for reuse. the solutestherein being neutralized bythe addition of an alkaline liquor. The digester is then filled up (as,for example, by means of the connection 32) with precipitated limewater, and

coils.

After this last cooking with precipitated lime water, the pulp may beblown into a blow pit or other suitable draining medium in the usualmanner, viz., normally the blow oi! valve (not shown) at the bottom ofthe digester is opened and. the as I contents of the digester are forcedout by the pressure existing therein. In some cases it is possible tocarry out the alkaline cook in the blow pit or elsewhere, after thestock has left the digester. The liquor that drains oil from the 8 blowpit is conducted to settling or clarifying tanks for reuse.

The precipitated lime water has a mildly alkaline reaction andneutralizes any ligno sulphonic acids which may remain in contact withthe cel- 35 lulose fibres after the acid cook. This action produces amuch stronger and more pliable pulp than that produced by the singlestage acid cook process and gives the pulp many characteristics ofkrait'pulp which'is produced by the alkaline 40 process.

The strength and folding of the pulp may be varied by varying the pointin the digestion process at which the precipitated lime (or otheralkaline) water is applied. For

example, if a pulp is desired having strength characteristics nearly thesame as ordinary sulphite pulp, the seco'ndstsge, or bisulpbite cook,

of my process is continued longer and at a higher temperature. If a pulpof much greater strength is desired, this cook is stopped and the acidremoved from the digester as soon as deteriorating compoundsappearandthelimewatercookis continued for a comparatively longer time.

Theterms lime water" and "precipitated lime to wa,"areusedinthisspecificstionandinthe appended claims to refer to aliquor which may or may notcontain considerable ma nesium in addition tothe calcium present.

The applicability of my process is not limited .0 to the spruce,hemlockahd fir ordinarily used for the production of sulphite pulp.

By my process I am able to produce a novel. sulphite pulp having anunusually high mullen,

tear and fold test, but much more pliable than 06 a kraft pull).

nor with fresh liquor for reuse, digesting the II fibrom material underheat and presure in bisulphite liquor until the lignin is substantiallyremoved therefrom, withdrawing bisulphiteliqnor from the material andmingling it with fresh liquor for reuse, and cooking the fibrousmaterial in alkaline liquoruntil the incrustants of the cellulose aresubstantially removed.

2. A process for the production of pulp which comprises soaking fibrousmaterial in heated bisulphite liquor under pressure until theextractives are substantially removed therefrom and the material is ofuniform moisture content, withdrawing the bisulphite. liquor andmingling it with 'fresh liquor or reuse, digesting the fibrous materialin bisulphite liquor under heat and pressure until deterioratingcompounds appear and thereupon draining liquor from the material andcooking the material in-alkaline liquor. I

3. A process for theproduction of pulp which comprises soaking fibrousmaterial in bisulphite liquor until the extractives are removedtherefrom and the liquor has penetrated the chips, draining oil thebisulphite liquor and mingling it with fresh liquor for reuse, digestingthe fibrous material in bisulphite liquor imder heat and pressure toremove lignin therefrom, draining oiI- liquor from the material, andfinally cooking the material in precipitated lime water.

4., A process for theproduction of sulphite pulp which comprises soakingfibrous material in bi sulphite liquor, draining off the liquor,digesting I said material under heat and pressure in additionalbisulphite liquor, and finally cooking said material in alkaline liquor.

5. A process for the production of sulphite pulp which comprises firstsoaking wood chips in' bisulphite liquor under pressure, then cookingthe chips in bisulphite. liquor under pressure at a temperature above100 C., and finally cooking in precipitated lime water.

6. In the production of sulphite pulp, charging a digester with fibrousmaterial, filling the charged digester with bisulphite liquor from anaccumulator and soaking the fibrous material in the digester under heatand pressure untfl the extractives' are substantially put into solution,withdrawing liquor from the digester and returning it to theaccumulator, refilling the digester with bisulphite liquor from theaccumulator and digesting the fibrous material in the digester underheat and pressure to remove lignin therefrom, withdrawing liquor fromthe digester, adding. alkaline liquor to the digester and cook-- ing thefibrous material in such alkaline liquor.

7. In the productionoi sulphite pulp, charging a digester with fibrousmaterial, filling the charged digester with bisulphite liquor andsoaking the fibrous material therein under pressure, withdrawing liquorfrom the digester, refilling the digester with bisulphite liquor anddigesting the fibrousmaterial therein under heat and pressure, againwithdrawing liquor from thedigester, admitting precipitated lime waterthereto and cookingthematerial therein.

8. In a process for the production of pul soaking fibrous material inbisulphite quor under heat and pressure until are substantially removedtherefrom andtheliquorhas penetratedthechips,dralnlngliquorfl'omthefibrous material, then subiectingthe fibrousmaterialtoaseriesoi'digestionpmcessesinbisulphite liquorimderheatandpressuraandfinallycookingthefibrousmaterialinalkalineliquor.

9. Inaprocessfottheprodutitlmofpulmsoab. ing fibrousmaterial'mbuulphiteliquor under heat and pressure until the extractivesare substantially removed therefrom, then subjecting the fibrousmaterial to a series of digestion processesunder pressure and atsuccessively higher temperatures, and finally cooking the fibrousmaterial in alkaline liquor. I

10. In a process for the production of pulp, charging a digester withfibrous material and soaking said material therein in bisulphite liquorunder heat and pressure to remove extractives therefrom, withdrawingliquor from the digester, refilling the digester with bisulphite liquorand digesting the fibrous material therein under heat and pressure toremove lignin therefrom, dis? charging the fibrous material from thedigester and thereafter cooking thefibrous material'in alkaline liquor.V

ii. A process for the production of sulphite pulp which comprises firstsoaking fibrous material in bisulphite liquor under heat and pressureuntil extractives are substantially removed therefrom and the materialis of uniform moisture content, then digesting the fibrous material inbisulphite liquor under heat and pressure until the formation of lignosulphonlc acid reaches a point deleterious to the material, and finallycooking the fibrous material in alkaline liquor until the incrustants ofthe cellulose are substantially removed therefrom.

12. Sulphite pulp obtained by soaking fibrous material in heatedbisulphite liquor under pressure until'the extractives are substantiallyput into solution and the bisulphite has penetrated the fibrousmaterial, withdrawing said liquor, cooking the material in freshbisulphite liquor under heat and pressure, withdrawing said liquor, andcooking the material in alkaline liquor.

13. A process for the production of pulp which comprises charging adigester with fibrous ma- Y terial, introducing hot acid liquor to the"digester while venting air therefrom, sealing the digester and forcingin additional quantities of the hot liquor to establish a highhydrostatic pressure on the liquor; maintaining the hot high pressureliquid in contact with the material until such liquid has substantiallycompletely penetrated 'the material, then draining the liquor from thesealed digester; introducing another batch of hot digestion liquor tothe digester and raising the mass to reaction temperatures.

14. A process for the production of pulp which comprises charging adigester'with fibrous material, establishing a body of hot liquor in aseparatefeceptac'le, introducing the hot liquor from the receptacle intothe digester while venting air from the digester, sealing the digesterand forcing in additional quantities of the hot liquor to establish a.high hydrostatic pressure on the liquor; maintaining the hot high'pressure liquor incontact'with the material until the liquor haspenetrated the material, then draining the liquor from the bottomportion of the digester. while maintaining the upper portion of thedigester sealed, mixing such drained liquor with fresh liquor for reuse;admitting further quantities of hot liquor from the receptacle intwthedigester and raising the mass to reaction temperatures.

15. A process for the production of pulp which comprises soakingfibrousmaterial in' heated bisulphite liquor under a pressure of theorder of fifty pounds, maintaining the liquor in contact with thematerial until it has substantially completely penetrated the material,then draining the liquor from the material, while preventing access ofair to the material, subsequently contacting 15 the soaked material withadditional quantities of hot liquor and raising the liquor to reactiontemperatures.

16. A method of treating fibrous material which comprises introducing amass of the material to a digester, forcing a quantity of hot digestionliquor into the digester while displacing air from the upper part of thedigester, sealing the upper part of the digester and forcing inadditional quantities of the hot liquor until a high hydrostaticpressure is established on the liquor; maintaining the hot high pressureliquor in contact with the material for a period of time sumciently longto effect saturation of the material, and to extract certain of theconstituents of the material, then withdrawing the liquor from thebottom of the digester while maintaining the top SeaIed admitting freshhot digestion liquor into the bottom of the digester and then raisingthe mass to reaction temperatures.

17. In the digestion of fibrous material, charging a digester withfibrous material, then admitting a hot digesting liquor while expellingair from the digester, sealing the digester after the expulsion of theair and admitting additional quantities of the liquor to establish ahigh hydrostatic pressure on the liquor; maintaining the fibrousmaterial in contact with the liquor until it is saturated thereby; thendraining the excess liquor from the digester and admitting fresh hotliquor, and cooldng the fibrous material in such fresh liquor.

18. In the digestion of fibrous material, charging a digester withfibrous material, admitting hot acid liquor to the digester whileexpelling air therefrom, forcing in a sufficient volume of the liquor toestablish a hydrostatic pressure of the order of fifty pounds,maintaining the liquor in contact with the material until theextractives are solubilized and the material is permeated with theliquor; then draining the excess liquor from the digester and admittingfresh hot liquor and digesting the material in such fresh liquor atelevated temperature and pressure.

19. In the digestion of fibrous material, charging a digester withfibrous material, admitting hot acid liquor, to the bottom of thedigester while displacing air from the top of the digester; sealing thetop of the digesterafter the expulsion of air and forcing in additionalquantities of the hot liquor to establish a hydrostaticpressure of theorder of fifty pounds on the liquor; maintaining the hot high pressureliquor in contact with the fibrous material until such material issaturated; then draining the liquor from the bottom of the digesterwhile maintaining the top sealed and after such drainage introducingfresh hot acid liquor to the digester and cooking the material undercooking temperature and pressure.

THOMAS LEONIDAS DUNBAR. 3

